Electromagnetic shielding sheet

ABSTRACT

An electromagnetic shielding sheet  1  includes: a transparent base  11 , and at least an adhesive layer  13 , an antirust layer  25 A and a mesh metal layer  21  formed on one of the surfaces of the base. A blackened layer  23 A is sandwiched between the mesh metal layer  21  and the antirust layer  25 A. At least openings  105  of the mesh metal layer  21  are filled up with a resin such that the mesh metal layer  21  has a substantially flat surface.

TECHNICAL FIELD

The present invention relates to a sheet for shielding electromagneticradiation and, more specifically, to an electromagnetic shielding sheetprovided with a meshed, thin metal foil (thin film), intended to bedisposed in front of a display, such as a cathode-ray tube (CRT) or aplasma display panel (PDP), to shield electromagnetic radiationgenerated by the display, and capable of enabling the satisfactoryvisual recognition of images displayed by the display.

BACKGROUND ART

Summary of Techniques: Problems attributable to electromagneticinference (EMI) have increased with the recent functional progress andspread of electric and electronic devices. Electromagnetic noise isclassified roughly into conducted noise and radiated noise. Methods ofpreventing problems due to conducted noises filter conducted noise by anoise filter. Methods of preventing problems due to radiated noise use ametal case to shield a space electromagnetically, place a metal sheetbetween wiring board, or coat the wires of cables with a metal foil.Although effective in electromagnetically shielding circuits and powerblocks, these methods are unsuitable for shielding electromagneticradiation generated by the screens of displays, such as CRTs and PDP,because those methods use opaque means.

The PDP is an assembly of a glass panel provided with data electrodesand a fluorescent layer, and a glass panel provided with transparentelectrodes. The PDP generates a large amount of electromagneticradiation, a large amount of near-infrared radiation and a large amountof heat when operated. Usually, a front panel is disposed in front ofthe PDP to shield electromagnetic radiation. The front panel must have ashielding function of 30 dB or above in the range of 30 MHz to 1 GHz toshield electromagnetic radiation emitted from the screen of the display.Infrared radiation of wavelengths in the range of 800 to 1,100 nmradiated from the screen of the display must be shielded becauseinfrared radiation makes other devices, such as a remote controller forthe remote control of VTRs and air conditioners, malfunction. Theelectromagnetic shielding metal mesh (lines) of the electromagneticshielding sheet should not deteriorate visibility and theelectromagnetic shielding sheet must have proper transparency (visiblelight transmitting property, visible light transmittance) to make imagesdisplayed by the display satisfactorily visible.

Since the PDP is provided with a large screen, such as a 37 in. screen,a 42 in. screen or a larger one, the electromagnetic shielding sheetused in combination with the PDP has thousands of horizontal andvertical lines defining openings. Since parts of an adhesive layer areexposed in the openings of the electromagnetic shielding sheet, theadhesive layer exposed to the adverse effects of an etchant duringetching is colored, and the adhesive layer is deteriorated by analkaline resist remover for removing a resist film after etching.

Prior Art: To ensure improved visibility of displayed images, the frontpanel is required to have a uniform, stable mesh structure capable ofelectromagnetic shielding, having proper transparency (visible lighttransmittance), not colored in an undesired color and not subject topeeling.

A front panel having a mesh structure disclosed in JP 5-283889 A has thefollowing structure: (base)/(transparent anchor layer)/(electromagneticshielding layer). The electromagnetic shielding layer has a meshedpattern and is formed by an electroless plating process. A method offorming a metal mesh for an electromagnetic shielding sheet disclosed inJP 09-293989 A uses a photoresist process. An electromagnetic shieldingstructure disclosed in JP 10-335885 A is formed by laminating a plasticfilm provided with a copper foil formed in a geometrical pattern byphotolithography to a plastic plate. Although those prior artelectromagnetic shielding sheets formed by the prior art methods have amesh structure, only the metal mesh is coated with an antirust layer,and the antirust layer is not formed over the entire base and theadhesive layer. The prior art methods mention nothing about forming theantirust layer over the entire base and the adhesive layer. Generally,the electromagnetic shielding sheet is disposed with the base facing theviewing side. Therefore, it is difficult to connect a groundingelectrode of the electromagnetic shielding sheet to a ground.

An electromagnetic shielding sheet disclosed in JP 11-298185 having astructure (transparent base)/(black layer)/(patterned metallayer)/(antirust layer) is formed by a patterning method of forming apattern (a meshed pattern, as in the present invention) that superposesa black layer and a patterned metal layer on a patterned resist film,washes off the black layer and the patterned metal layer together withthe resist film, and then forms the antirust layer. However, theantirust layer cannot be formed between the transparent base and theblack layer or the metal layer, or in openings. Furthermore the minutemeshes cannot be precisely formed because the pattern (the meshedpattern) is not formed by an etching process. Parts of an adhesive layeror the base exposed in the openings to form transparent parts arecolored or yellowed by the agency of an etchant used in the corrodingprocess. Such colored parts affect the color tone of displayed images,and the coloring of those parts reduces the adhesive strength of theadhesive layer. In some cases, metal ions, such as Fe³⁺ ions, containedin the etchant and penetrated into the adhesive layer and the basedeteriorate coloring matters added to the adhesive for color correctionand infrared ray absorption. When an electromagnetic shielding sheet isbonded to a transparent base or the screen of a display with anadhesive, bubbles B remain in the openings in the mesh structure asshown in FIG. 7, and light is scattered at the interface between thebubbles and the adhesive to increase haze value. A filter disclosed inJP 2000-227515 A is formed by laminating a near-infrared absorbingfilter to the foregoing electromagnetic shielding sheet, and has both anelectromagnetic shielding ability and a near-infrared absorbingproperty.

An electromagnetic shielding sheet fabricating method of fabricatingthis prior art filter needs an additional process for bonding thenear-infrared absorbing filter to the electromagnetic shielding sheetwith an adhesive.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the above problems and itis therefore an object of the present invention to provide aninexpensive electromagnetic shielding sheet disposed in front of adisplay, such as a CRT or a PDP, capable of shielding bothelectromagnetic radiation and near-infrared radiation, not subject tothe increase of haze value due to bubbles remaining in an adhesivelayer, and capable of ensuring the high visibility of displayed images.

According to the present invention, an electromagnetic shielding sheetincludes: a transparent base; a transparent antirust layer formed on oneof the surfaces of the base; and a mesh metal layer formed on theantirust layer and having lines defining openings; wherein the antirustlayer extends over parts of the base corresponding to both the lines andthe openings.

The electromagnetic shielding sheet according to the present inventionis disposed in front of a display, such as a PDP, to shieldelectromagnetic radiation generated by the display, is provided with themesh metal layer having invisible lines and having both anelectromagnetic shielding ability and a transparency, may be disposedwith either of the surfaces thereof facing a viewing side, has anadhesive layer and the base scarcely subject to discoloration andqualitative changes and deterioration, and not peeled off by an etchingprocess and a resist film removing process during fabrication, and iscapable of ensuring the high visibility of images for a long period oftime.

In the electromagnetic shielding sheet according to the presentinvention, the lines of the mesh metal layer have a width in the rangeof 5 to 25 μm and are arranged at pitches in the range of 150 to 500 μm.

According to the present invention, the lines of the mesh metal layerare invisible and have both an electromagnetic shielding ability and ahigh transparency.

In the electromagnetic shielding sheet according to the presentinvention, a blackened layer is formed on one of the surfaces of themesh metal layer.

According to the present invention, the lines of the mesh metal layerare invisible and enable images to be viewed in high visibility.

The electromagnetic shielding sheet according to the present inventionfurther includes an additional antirust layer formed on one surface ofthe mesh metal layer opposite the other surface of the same facing thebase.

The electromagnetic shielding sheet may be disposed with the surface ofthe base facing a PDP, reduces work for connecting electrodes, does notneed any printed black frame, and does not glare to spoil the visibilityof images.

In the electromagnetic shielding sheet according to the presentinvention, the openings in the mesh metal layer are filled up with atransparent resin such that the surface of the transparent resin isflush with the surface of the mesh metal layer.

Since the openings in the mesh metal layer are filled with thetransparent resin, the electromagnetic shielding sheet is easy tohandle.

In the electromagnetic shielding sheet according to the presentinvention, the transparent resin filling up the openings in the meshmetal layer contains a color tone correcting light-absorbing agentcapable of absorbing visible light having wavelengths between 570 to 605nm and/or a near-infrared-absorbing agent capable of absorbing infraredradiation having wavelengths between 800 to 1100 nm.

The electromagnetic shielding sheet according to the present inventionfurther includes a layer of a color tone correcting agent capable ofabsorbing visible light having wavelengths in the range of 570 to 605 nmand/or a layer of a near-infrared-absorbing agent capable of absorbingnear-infrared radiation having wavelengths in the range of 800 to 1100nm formed on the outer surface of either the base or the additionalantirust layer.

The electromagnetic shielding sheet according to the present inventionshields both near-infrared radiation and electromagnetic radiationgenerated by the PDP to prevent problems due to near-infrared radiationand electromagnetic radiation, permits visible light to permeate,absorbs light of colors between yellow and orange in the emissionspectrum of neon atoms generated by the PDP to prevent images from beingcolored in an orange color tone, and ensures the satisfactory visibilityof displayed images.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an electromagnetic shielding sheet according tothe present invention;

FIG. 2 is a partial, typical perspective view of the electromagneticshielding sheet according to the present invention;

FIG. 3A is a sectional view taken on the line A-A in FIG. 2;

FIG. 3B is a sectional view taken on the line B-B in FIG. 2;

FIG. 4 is a sectional view of assistance in explaining the constructionof a conductive structure;

FIG. 5A is a plan view of assistance in explaining a method ofprocessing a rolled continuous film;

FIG. 5B is a side elevation of assistance in explaining the method ofprocessing a rolled continuous film;

FIG. 6 is a sectional view of an electromagnetic shielding sheetaccording to the present invention to be applied to the screen of adisplay;

FIG. 7 is a sectional view of an electromagnetic shielding sheetprovided with a cover; and

FIG. 8 is a view of assistance in explaining a method of fabricating anelectromagnetic shielding sheet.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will be described withreference to the accompanying drawings.

The present invention is not limited in its practical application to theembodiment specifically described herein.

FIG. 1 is a plan view of an electromagnetic shielding sheet according tothe present invention.

FIG. 2 is a partial, typical perspective view of the electromagneticshielding sheet according to the present invention.

General Construction: Referring to FIG. 1, an electromagnetic shieldingsheet 1 according to the present invention includes a transparent base11, a mesh structure 103 formed on the base 11, and a grounding frame101 surrounding the mesh structure 103. As shown in FIG. 2, the meshstructure 103 has intersecting lines 107 defining a plurality ofopenings (cells) 105. The grounding frame 101 is grounded when theelectromagnetic shielding sheet 1 is combined with a display.

The lines 107 are bonded to one surface of the transparent base 11 withan adhesive layer 13. The lines 107 are formed by processing a laminatedconductive structure 109. When the conductive structure 109 can beformed directly on the base 11 by electroless plating or vacuumevaporation, the adhesive layer 13 may be omitted. The lines 107intersect each other to form openings 105 in a close arrangement in aplane.

Thus, the mesh structure 103 has the lines 107 and the openings 105. Asshown in FIG. 2, the width of the lines 107 is referred to as line widthW, and the distance between the similar edges of the adjacent lines 107is referred to as pitch P.

FIGS. 3A and 3B are sectional views taken on the lines A-A and B-B inFIG. 2, respectively.

FIG. 4 is a sectional view of assistance in explaining the constructionof the conductive structure.

Construction of Conductive Structure:

As shown in FIG. 3A showing a section in a plane crossing the openings105, the openings 105 and the lines 107 are arranged alternately. Asshown in FIG. 3B showing a section in a plane including the line 107,the continuous line 107 is formed from the conductive structure 109. Asshown in FIGS. 3A, 3B and 4, the conductive structure 109 has a metallayer 21 and, preferably, at least a blackened layer 23A or 23B formedon a surface of the metal layer 21 facing a viewing side. Morepreferably, the conductive structure 109 has an antirust layer 25Aand/or an antirust layer 25B formed on the blackened layer 23A and/orthe blackened layer 23B. An antirust layer may be formed at least on theblackened layer 23A. The antirust layer 25A that extend also in theopenings 105 of the mesh structure is transparent. The antirust layer25B formed only on the lines 107 of the mesh structure may be eithertransparent or opaque.

The antirust layers 25A and 25B prevent the metal layer 21 and theblackened layers 23A and 23B from rusting, and prevent the blackenedlayers 23A and 23B from coming off. The antirust layers 25A and 25Bprotects the adhesive layer 13 adhesively bonding the conductivestructure 109 to the base 11. When necessary, the blackened layer 23Band the antirust layer 25B, i.e., an additional antirust layer 25B, maybe formed on the other surface of the metal layer 21, and the blackenedlayer 23A and 23B and the antirust layers 25A and 25B may be formed onboth the surfaces of the metal layer 21, respectively. Most preferably,the blackened layer 23A and the antirust layer 25A are formed on thesurface of the metal layer 21 facing the viewing side.

POINTS OF THE INVENTION

In a prior art technique, the metal layer 21 and the antirust layer areetched to leave only parts of the antirust layer 25A on the lines 107.In the present invention, the metal layer 21 is etched so that parts ofthe antirust layer 25A also remain on the base 11 in the openings 105 ofthe mesh structure. Thus, the antirust layer 25A extending over theentire surface of the base 11 protects the adhesive layer 13. Accordingto the prior art technique, parts of the adhesive layer 13 exposed inthe openings 105. The exposed parts of the adhesive layer 13 are exposedto the adverse effects of an etchant during etching and are colored, theadhesive layer 13 is deteriorated and altered by an alkaline resistremover for removing a resist film after etching and, consequently, theadhesive strength of the adhesive layer 13 decreases. According to thepresent invention, the adhesive layer 13 is protected from the foregoingadverse effects of etching and the associated processes by the antirustlayer 25A. Thus, the antirust layer 25A can prevent the contamination ofthe adhesive layer 13 with iron and sodium contained in the etchant, andprevents the discoloration and fading of the light-absorbing agent.

In most cases, the electromagnetic shielding sheet 1 is disposed withits base 11 facing the viewing side. In the electromagnetic shieldingsheet 1 of the present invention, the antirust layer 25A is formed onthe blackened layer 23A or, when necessary, the antirust layers 25A and25B of the same quality are formed on both the blackened layers 23A and23B. Since the blacking layer 23B formed on the surface of the metallayer 21 not facing the base is protected by the antirust layer 25B,particles contained in the blackened layer 23B do not come off easily.Thus, electromagnetic shielding sheet 1 may be disposed with either ofthe opposite surfaces thereof facing the viewing side. If theelectromagnetic shielding sheet 1 is disposed with the metal layer 21facing the viewing side, the grounding frame 101 (an electrode infunction) is exposed, the grounding frame 101 can be easily connected toa ground. The very thin antirust layer (additional antirust layer) 25Band the very thin blackened layer 23B do not obstruct grounding. Thegrounding frame 101 is formed by a blackening treatment. The groundingframe 101 may be formed simultaneously with the blackened layer 23A or23B by a blackening treatment for forming the blackened layer 23A or23B, which reduces processes and costs.

Although the electromagnetic shielding sheet 1 is supposed to be used incombination with a display, such as a CRT or a PDP herein, naturally,the electromagnetic shielding sheet 1 can be used for electromagneticshielding in combination with an apparatus other than displays.

The PDP is featured by its large screen. The dimensions of theelectromagnetic shielding sheet 1 are on the order of 620 mm×830 mm fora 37 in. screen, and on the order of 580 mm×980 for a 42 in. screen. Theelectromagnetic shielding sheet 1 can be formed in greater dimensions.Usually, the respective numbers of the horizontal and the vertical linesof the electromagnetic shielding sheet are several thousands. The linesmust be formed in a predetermined region in the line width W in anaccuracy on the order of micrometers. A person viewing images displayedby the display feel a feeling of very strong wrongness if parts of theelectromagnetic shielding sheet 1 corresponding to the openings 105 arecolored in an undesired color. In the electromagnetic shielding sheet ofthe present invention, the transparent antirust layer 25A extending overthe entire surface of the mesh structure including the openings 105prevents the adhesive layer 13 or the base 11 from being colored, andhas an electromagnetic shielding ability and a moderate transparency.Thus, the electromagnetic shielding sheet of the present inventionensures the excellent visibility of displayed images. The antirust layer25A has a refractive index different from that of the adhesive layer 13or a flattening layer 29. The refractive index of the antirust layer 25Ais relatively large, the refractive index of the adhesive layer 13 orthe flattening layer 29 is relatively small. Thus, it is expected thatthe antirust layer 25B exercises optical effects, such as anantireflection effect and a contrast enhancing effect.

The laminated conductive structure 109 of the electromagnetic shieldingsheet 1 includes the metal layer 21, the blackened layer 23A and/or theblackened layer 23B formed at least on one of the surfaces of the metallayer 21, and the antirust layer 25A and/or the antirust layer 25Bforming the surface of the conductive structure 109 facing the base 11.The antirust layer 25A extends over the entire surface of the base 11including parts corresponding to the lines and the openings.

The conductive structure 109 is subjected to a photolithographic processto form the mesh structure after being bonded to the transparent base 11with the adhesive layer 13. Then, a transparent resin is spread over themesh structure to form the flattening layer 29 filling up the openings105 and having a flat outer surface. Light-absorbing layers 31A and 31Bcapable of absorbing near-infrared radiation having wavelengths in aspecific wave band, or near-infrared radiation and visible light havingwavelengths in a specific wave band are formed on the surfaces of thebase 11 and the flattening layer 29 when necessary. The electromagneticshielding sheet disposed in front of the display shields electromagneticradiation and near-infrared radiation generated by the display. Theadhesive layer does not contain any bubbles that cause haze andwhitening, the mesh structure has a uniform density, black or white spotdefects and lines are very few, the electromagnetic shielding sheet hasmoderate transparency, and displayed images are visible in satisfactoryvisibility.

Fabricating Method:

In fabricating the electromagnetic shielding sheet 1 of the presentinvention, the conductive structure 109 provided at least with theblackened layer on the viewing side, and the antirust layer on the sideof the base 11 is fabricated. The conductive structure 109 is laminatedto one of the surfaces of the base 11, i.e., a transparent film, withthe adhesive, and a resist film 109 a having a meshed pattern is formedover the conductive structure 109. A photolithographic process iscarried out to remove parts of the conductive structure 109 not coatedwith the resist film 109 a excluding the antirust layer 25A by etchingand then the resist film 109 a is removed. The electromagnetic shieldingsheet can be fabricated by existing fabricating apparatuses and most ofthe processes can be successively carried out. Thus, the electromagneticshielding sheet can be fabricated in a high quality at a high yield rateand at a high production efficiency (FIG. 8).

Materials of the layers of the electromagnetic shielding sheet 1 of thepresent invention will be described.

Conductive Structure:

The conductive structure 109 for shielding electromagnetic radiation hasthe metal layer 21 formed of a metal having a conductivity sufficientfor shielding electromagnetic radiation, such as gold, silver, copper,iron, nickel or chromium. The metal layer 21 may be a single layer or alaminated layer, and may be formed of an alloy. Iron base metalssuitable for forming the metal layer 21 are low-carbon steels, such aslow-carbon rimmed steels and low-carbon aluminum-killed steels, Ni—Fealloys, and Invar. When cathodic electrodeposition is used, copper orcopper alloy foils are desirable. The copper foils may be rolled copperfoils and electrolytic copper foils. Electrolytic copper foils arepreferable because electrolytic copper foils have a uniform thickness,have a satisfactory property to adhere to blackened layers and/or layersformed by a chromate treatment, and are capable of being formed in thinfilms of a thickness not greater than 10 μm. The thickness of the metallayer 21 is in the range of about 1 to about 100 μm, preferably, in therange of 5 to 20 μm. Although the metal layer 21 can be easily processedby photolithography to form the mesh structure if the thickness of themetal layer 21 is less than the lower limit of the thickness range, amesh structure formed by processing the metal layer 21 having such asmall thickness has a large electrical resistance that reduces theelectromagnetic shielding effect. If the metal layer 21 has a thicknessgreater than the upper limit of the thickness range, a desired fine meshstructure cannot be formed and, consequently, the mesh structure has alow real ratio of open area and a low transmittance, visual angledecreases, and the visibility of images becomes low. The metal layer 21is formed beforehand and is bonded to the base 11 with the adhesivelayer 13. The metal layer 21 may be formed directly on the base 11 by anelectroless plating process, an electroless plating and an electrolyticplating process or a vacuum deposition process. The adhesive layer 13can be omitted when the metal layer 21 is formed directly on the base11.

Preferably, the metal layer 21 has a surface roughness Rz between 0.5 to10 μm. The metal layer 21 reflects external light in a specularreflection mode deteriorating the visibility of images if the surfaceroughness thereof is below 0.5 μm even if the surface of the metal layer21 is blackened. The adhesive and the resist cannot be uniformly spreadover the entire surface of the metal layer 21, bubbles are formed in theadhesive and the resist if the surface roughness of the metal layer 21is greater than 10 μm. The surface roughness Rz is the mean of roughnessvalues of ten points measured by a surface roughness measuring methodspecified in B0601, JIS.

Blackening Treatment:

The surface, facing the viewing side, of the metal layer 21 of themeshed conductive structure 109 needs to be processed by a blackeningtreatment to improve the visibility of images and to increase contrastin images by absorbing external light falling on the electromagneticshielding sheet 1. The blackening treatment roughens and/or blackens thesurface of the metal layer 21. The blackening treatment can be achievedby any one of various methods. For example, the blackening treatment canform a metal oxide or a metal sulfide over the surface of the metallayer 21. If the metal layer 21 is formed of iron, an oxide film(blackening film) of a thickness between 1 to 2 μm is formed by exposingthe metal layer 21 to steam of a temperature in the range of 450° C. to470° C. for a period in the range of 10 to 20 min. An oxide film(blackening film) may be formed by chemically processing the metal layer21 with a chemical, such as concentrated nitric acid. If the metal layer21 is a copper foil, it is preferable to attach cationic particles tothe metal layer 21 by an electrodeposition process using an electrolyticsolution containing sulfuric acid, copper sulfate and cobalt sulfate.The cationic particles adhering to the surface of the metal layer 21increases the surface roughness of the metal layer and blackens thesurface of the metal layer 21. The cationic particles may be copperparticles or copper alloy particles. Copper-cobalt alloy particles arepreferable.

In this specification, the blackening treatment includes roughening andblackening. Preferably, a preferable blackening density is 0.6 or above.Blackening density is measured by using COLOR CONTROL SYSTEM GRETAGSPM100-11® (Kimoto Co.). Measurement of the blackening density of aspecimen uses an angle of observation field of 10°, a light source D50,and an illumination type T specified in the ANSI standards. Theblackening density of the specimen is measured after white calibration.Preferably, the reflectance of the surface processed by the blackeningtreatment is 5% or below. Reflectance is measured by using Haze MeterHM150® (Murakami Sikisai) by a method specified in K7105, JIS.

Alloy Particles:

The cationic particles may be copper particles or copper alloyparticles. Preferably, the cationic particles are copper-cobalt alloyparticles. Copper-cobalt alloy particles can improve blackening degreeremarkably and absorb visible light satisfactorily. The opticalcharacteristics representing the image visibility improving effect ofthe electromagnetic shielding sheet are expressed by the color system“L*, a*, b*, ΔE*” specified in Z8729, JIS. The conductive structure 109becomes more invisible when the absolute values of a* and b* aresmaller. Consequently, contrast in images is enhanced and the visibilityof images is improved. The effect on decreasing the values of a* and b*of the copper-cobalt alloy particles, as compared with that of copperparticles, is high. The copper-cobalt alloy particles are able toreduces the values of a* and b* near to zero.

Preferably, the mean particle size of the copper-cobalt alloy particlesis in the range of 0.1 to 1 μm. Copper-cobalt alloy particles having amean particle size exceeding the upper limit of the desired rangereduces the thickness of the metal layer 21 excessively and,consequently, it is possible that the copper foil is broken inlaminating the same to the base 11, and the surface of the metal layer21 lacks fineness and has an uneven appearance because the particles arenot formed compactly. Copper-cobalt particles having a mean particlesize below the lower limit of the range lack roughening effect and hencethe visibility of images is unsatisfactory.

Antirust Layer:

The antirust layer 25A and/or the antirust layer 25B is formed at leaston the blackened layers 23A and 23B formed by blackening the metal layer21 to prevent the metal layer 21 and/or the blackened layers fromrusting and to prevent the blackened layers from coming off and beingdeformed. The antirust layers 25A and 25B may be layers of oxides ofnickel and/or zinc and/or copper or layers formed by a chromatetreatment. The layers of oxides of nickel and/or zinc and/or copper canbe formed by a known plating process. The thickness of the layers ofoxides of nickel and/or zinc and/or copper is in the range of about0.001 to about 1 μm, preferably, in the range of 0.001 to 0.1 μm.

Chromate Treatment:

The chromate treatment treats a workpiece with a chromating solution.The chromating solution may be applied to the workpiece by aroll-coating method, a curtain-coating method or a squeeze-coatingmethod. The workpiece may be wetted with the chromating solution by adipping method. The workpiece treated by the chromate treatment is driedwithout rinsing. A coating method, such as a roll-coating method, ispreferable when only one of the surfaces of the workpiece is to betreated by the chromate treatment. A dipping method is preferable whenboth the surfaces of the workpiece are to be treated by the chromatetreatment. Usually, the chromating solution is a CrO₂ solution having aCrO₂ concentration of 3 g/l. A chromating solution obtained by adding anoxycarboxylic compound to a chromic anhydride solution to reduce part ofhexavalent chromium into tervalent chromium may be used. The surface ofthe workpieces treated by the chromate treatment is colored in a colorof a color category including light yellow and yellowish brown dependingon the amount of deposited hexavalent chromium. Since tervalent chromiumis colorless, a film formed by the chromate treatment has practicallyacceptable transparency when the ratio between the respective amounts oftervalent chromium and hexavalent chromium is controlled properly.Suitable oxycarboxylic compounds are tartaric acid, malonic acid, citricacid, lactic acid, glycolic acid, glyceric acid, tropic acid, benzilicacid and hydroxyvalerianic acid. Those chemicals may be usedindividually or in combination. Since the different compounds havedifferent reducing effects, the amount of the compound added to thechromic anhydride solution must be determined according to the rate ofreduction of hexavalent chromium into tervalent chromium.

More concretely, suitable chromating agents are, for example, ALSURF100® commercially available from Nippon Paint Co. and PM-284®commercially available from Nippon Parkerizing Co. The chromatetreatment is particularly effective in enhancing the effect of theblackening treatment.

The blackened layers 23A and 23B may be formed at least on the viewingside, and the antirust layers 25A and 25B may be formed at least on theside of the base 11. Contrast is improved to improve the visibility ofdisplayed images. The blackened layers 23A and 23B and the antirustlayers 25A and 25B may be formed on the side of the display. Thus straylight emitted by the display can be shielded to improve the visibilityof images.

Subsequently, the transparent base 11 is bonded to the antirust layer25A with the adhesive layer 13.

Base:

The base 11 may be formed of any one of various materials, provided thatthe materials have desired transparency, desired insulating property,desired heat resistance and desired mechanical strength. Suitablematerials for forming the base 11 are, for example, polyester resinsincluding polyethylene terephthalate resins, polybutylene terephthalateresins, polyethylene naphthalate resins, polyethyleneterephthalate-isophthalate copolymers,terephthalate-cyclohexanedimethanol-ethylene glycol copolymers andpolyethylene terephthalate/polyethylene naphthalate resins forcoextrusion, polyamide resins including nylon 6, nylon 66 and nylon 610,polyolefin resins including polypropylene resins and poly(methylpentene) resins, vinyl resins including polyvinyl chloride resins,acrylic resins including polyacrylate resins, polymethacrylate resinsand poly(methylmethacrylate) resins, imide resins including polyimideresins, polyamidimide resins and poly(etherimde) resins, engineeringplastics including polyarylate resins, polysulfone resins, poly(ethersulfone) resins, polyphenylene ether resins, polyphenylene sulfideresins (PPSs), polyaramid resins, poly(ether ketone) resins, polyethernitrile resins, poly(ether ether ketone) resins and polyether sulfideresins, and styrene resins including polycarbonate resins andpolystyrene resins.

The base 11 may be formed of a copolymer containing some of theforegoing resins as principal components, a mixture of some of theforegoing resins or an alloy of some of the foregoing resins. The base11 may be a laminated sheet. Although the base 11 may be either anoriented film or an unoriented film, it is preferable, in view ofmechanical strength, that the base 11 is a uniaxially oriented film or abiaxially oriented film. The thickness of the base 11 is in the range ofabout 12 to about 1000 μm, preferably, in the range of 50 to 700 μm. Themost desirable thickness of the base 11 is in the range of 100 to 500μm. If the base 11 is excessively thin, the base 11 has an insufficientmechanical strength and warps or sags. If the base 11 is excessivelythick, the base 11 has an over quality and is uselessly expensive.

The base 11 is a film, a sheet or a board having at least one layer ofone of those resins. In this specification, a film, a sheet and a boardwill be referred to inclusively as “film”. Polyester films, such aspolyethylene terephthalate films and polyethylene naphthalate films, aresuitable films as the base 11 because polyester films are satisfactoryin transparency and heat resistance and inexpensive. Polyethyleneterephthalate films are most suitable. Although films having highertransparency are more desirable, films having a transparency of 80% orabove are acceptable.

The surface of the base 11 may be altered by surface treatment to renderthe surface receptive to the adhesive layer 13. The surface treatmentmay be corona discharge treatment, plasma treatment, ozone treatment,flame treatment, coating with a primer, i.e., anchoring agent, adhesionpromoting agent or adhesive receptivity improving agent, preheating,dust removing treatment, deposition treatment or alkali treatment. Whennecessary, the resin film may contain additives, such as a filler, aplasticizer and an antistatic agent.

Laminating Process:

The adhesive layer 13 formed on one of the surfaces of the conductivestructure 109, the adhesive layer 13 is dried if necessary, and the base11 is hot-pressed or cold-pressed against the surface of the conductivestructure 109 coated with the adhesive layer 13 to bond the base 11 tothe conductive structure 109 with the adhesive layer 13. When necessary,the assembly of the base 11 and the conductive structure 109 may besubjected to aging at a temperature in the range of 30° C. to 80° C.When the base 11 or the outermost layer of the laminated base 11 isformed of a heat-adhesive resin, such as an ionomer, an ethylene-vinylacetate copolymer, an ethylene-acrylic acid copolymer or anethylene-acrylate copolymer, the base 11 can be bonded to the conductivestructure 109 simply by hot-pressing.

Adhesive:

The adhesive layer 13 may be formed of any suitable resin, such as anacrylic resin, a polyester resin, a urethane resin, an epoxy resin or apolyvinyl chloride-acetate resin. Dry lamination using a thermosettingresin having satisfactory processability and resistant to the coloringand deteriorative effects of an etchant is preferable. Anionizing-radiation-curable resin that can be cured with ionizingradiation, such as ultraviolet radiation or electron beams, ispreferable. Suitable ionizing-radiation-curable resins are, for example,prepolymers (or oligomers) including polyester (meth)acrylate resins,urethane (meth)acrylate resins and epoxy (meth)acrylate resins, monomersincluding trimethylolpropane trimethacrylate resins anddipentaerythritol hexamethacrylate resins and mixtures of some of thoseresins. In this specification, “(meth)acrylate” signifies acrylate ormethacrylate.

Dry Lamination:

A dry lamination process for laminating two films forms adhesive layerson the films by applying an adhesive solution prepared by dissolving anadhesive in a solvent to the films and drying the adhesive solution,laminates the films to form a laminated film, subjects the laminatedfilm to aging at a temperature in the range of 30° C. to 120° C. forseveral hours to several days to cure the adhesive. A nonsolventlamination process developed by improving the dry lamination process maybe employed. The nonsolvent lamination process can spread an adhesiveinstead of the adhesive solution over films, dry the adhesive, laminatethe films in a laminated film and subjects the laminated structure toaging at a temperature in the range of 30° C. to 120° C. for severalhours to several days to cure the adhesive so that the films are bondedtogether.

An adhesive suitable for the dry lamination process or the nonsolventlamination process is a thermosetting adhesive or anionizing-radiation-curable adhesive that can be cured with ionizingradiation, such as ultraviolet radiation or electron beams. Suitablethermosetting adhesives are two-part adhesives, such as urethaneadhesives including polyester-urethane adhesives, polyether-urethaneadhesives and acryl-urethane adhesives, acrylic adhesives, polyesteradhesives, polyamide adhesives, polyvinyl acetate adhesives, epoxyadhesives and rubber adhesives. Two-part urethane adhesives arepreferable.

A suitable two-part urethane adhesive is, for example, an aromaticpolyisocyanate, such as tolylenediisocyanate, diphenylmethanediisocyanate or polymethylene polyphenylene polyisocyanate, or two-parturethane resin obtained by reacting polyfunctional isocyanate, i.e.,aliphatic or alicyclic polyfunctional isocyanate, such as hexamethylenediisocyanate, xylylene diisocyanate or isophorone diisocyanate, with ahydroxyl-terminated compound, such as polyether polyol, polyester polyolor polyacrylate polyol.

Preferable adhesive is obtained by mixing a polyester polyurethane resindenatured by a styrene-maleic acid copolymer resistant to the coloringand deteriorative effects of an etchant, and an aliphatic polyisocyanateresin.

The dry lamination process can dissolve or disperse an adhesivecomposition containing the foregoing materials as principal componentsin an organic solvent to produce an adhesive liquid, coat a film with afilm of the adhesive liquid by a coating method, such as a roll coatingmethod, a reverse-roll coating method, a gravure roll coating method, agravure reverse-roll coating method, a gravure offset coating method, akiss coating method, a wire bar coating method, a comma coating method,a knife coating method, a dip coating method, a flow coating method or aspray coating method, and dry the film of the adhesive liquid to removethe solvent. A roll coating method or a reverse-roll coating method ispreferable.

The thickness of the dry adhesive layer 13 is in the range of about 0.1to about 20 μm, preferably, in the range of 1 to 10 μm. The base 11 islaminated to the laminated conductive structure 109 immediately afterthe formation of the adhesive layer 13, and a laminated structure thusformed is subjected to aging at a temperature in the range of 30° C. to120° C. for several hours to several days to cure the adhesive layer 13so that the base 11 and the laminated conductive structure 109 arebonded together. The adhesive layer 13 may be formed on either the base11 or the laminated conductive structure 109. Preferably, the adhesivelayer 13 is formed on the copper foil so as to cover the roughenedsurface of the copper foil entirely to prevent formation of bubbles inthe laminated structure.

Although the nonsolvent lamination process and the dry laminationprocess are basically the same, the nonsolvent lamination process usesthe adhesive composition directly without dissolving or dispersing theadhesive composition in a solvent. When necessary, the adhesivecomposition is heated to decrease the viscosity of the adhesivecomposition.

Adhesive:

The adhesive may be a known pressure-sensitive adhesive. There are notparticular restrictions on the adhesive. The adhesive may be any one ofsuitable resins. Suitable adhesives are natural rubber, syntheticrubbers including butyl rubbers, polyisoplene rubbers, polyisobutylenerubbers, polychloroprene rubbers and styrene-butadiene copolymers,silicone resins including dimethyl polysiloxane resins, acrylic resins,vinyl acetate resins including polyvinyl acetate resins andethylene-vinyl acetate copolymers, urethane resins, acrylonitrileresins, hydrocarbon resins, alkylphenol resins, and rosin resinsincluding rosin, rosin triglyceride reins and hydrogenated rosin.

Rubber Adhesive:

Effective rubber adhesives are mixtures each of one or some of adhesivesincluding chloroprene rubber, nitrile rubber, acrylic rubber,styrene-butadiene rubber, styrene-isoprene-styrene rubber,styrene-butadiene-styrene rubber, styrene-ethylene-butadiene rubber,butyl rubber, polyisobutylene rubber, natural rubber and polyisoprenerubber, and one or some of tackfiers including phenol resins, modifiedphenol resins, ketone resins, alkyd resins, rosin resins, coumaroneresins, styrene resins, petroleum resins and vinyl chloride reins.

The rubber adhesives are superior to acrylic adhesives in chemicalresistance, swelling resistance, heat resistance, tackiness and peelingstrength. Therefore, layers bonded with the rubber adhesive will notpeel off even if the same are exposed to acid or alkali solutions. Therubber adhesive is scarcely subject to hydrolysis in acid or alkalisolutions, and maintains its adhesive property for a long time.

Adhesive Layer:

A latex, an aqueous dispersion or an organic solution of one or some ofthe foregoing resins is spread in an adhesive film on the surface of oneof two layers to be bonded together by a known printing method, such asa screen printing method or a comma coating method, or a known coatingmethod, the adhesive film is dried when necessary, and then the otherlayer is pressed against the former layer.

FIGS. 5A and 5B are a plan view and a side elevation, respectively, ofassistance in explaining a method of processing a rolled continuousfilm.

A roll of the continuous film is used for forming laminated structures.In FIG. 5, the electromagnetic shielding sheets 1 are formed atpredetermined intervals on the continuous film unwound from a roll. FIG.5B shows the conductive structure 109 laminated to the base 11. Theconductive structure 109 is formed by forming the antirust layer 25B,the blackened layer 23B, the metal layer 21, the blackened layer 23A andthe antirust layers 25A in that order on the continuous film unwoundfrom a roll. The adhesive layer 13 is formed on the antirust layer 25Aof the conductive structure 109 by spreading an adhesive in an adhesivefilm to the surface of the antirust layer 25A and drying the adhesivefilm. The conductive structure 109 is bonded to the base 11 by pressingthe same against the base 11. When necessary, a laminated structureformed by bonding together the conductive structure 109 and the base 11is aged (cured) at a temperature in the range of 30° C. to 80° C. forseveral hours to several days, and the laminated structure is wound in aroll 2.

Photolithography:

As shown in FIG. 8, a resist film 109 a having a predetermined meshedpattern is formed on the conductive structure 109 of the laminatedstructure, parts of the conductive structure 109 not coated with theresist film 109 a are removed by etching, and the resist film 109 a isremoved to complete a meshed laminated structure.

Masking:

The conductive structures 109 of the continuous laminated structureformed by bonding together the base 11 and the conductive structures 109and unwound from a roll are processed by photolithography to form meshedconductive structures 109. The continuous laminated structure isprocessed for masking, etching and resist film removal while the same iskept taut and fed continuously or intermittently.

Masking can form, for example, the photoresist film 109 a over theentire surface of the conductive structure 109 of the laminatedstructure, dry the photoresist film 109 a, put a mask having apredetermined pattern on the photoresist film 109 a, expose thephotoresist film 109 a through the mask in the predetermined pattern oflines defining meshes. If the photoresist forming the photoresist film109 a is a negative resist film, i.e., a resist that becomes resistantto a developer when exposed to light, the meshed pattern is formed so asto cover parts of the conductive structure 109 corresponding to theopenings and to expose parts of the same corresponding to the lines. Ifthe photoresist forming the photoresist film 109 a is a positive resist,i.e., a resist that becomes dissolvable in a developer, the mesh patternis formed so as to cover parts of the conductive structure 109corresponding to the lines and to expose parts of the same correspondingto the openings. Light emitted by a mercury lamp is used for exposure.The exposed photoresist film 109 a is developed, subjected to ahardening process and a baking process.

The resist film 109 a is formed on the surface of the conductivestructure 109 by applying the resist, such as casein, a PVA or gelatin,to the surface of the conductive structure 109 by a dipping method, acurtain coating method or a flow coating method while the laminatedstructure formed by laminating the base 11 and the conductive structures109 is unwound from a roll and fed continuously or intermittently. Theresist film 109 a may be formed by attaching a dry resist film to theconductive structure 109 instead of applying the liquid resist to theconductive structure 109. The baking temperature is in the range of 200°C. to 300° C. when a casein resist is used. It is preferable to bake thelaminated structure at the lowest possible temperature to prevent thelaminated structure from warping.

Etching Process:

The resist film 109 a is etched after masking the same with the mask. Aferric chloride solution and a cupric chloride solution, which are easyto circulate, are preferable for a continuous etching process.Basically, the etching process is similar to an etching process using ashadow mask forming system for etching a continuous thin steel sheet ofa thickness in the range of 20 to 80 μm to form shadow masks for CRTs ofcolor TV sets. The etching process can be carried out by an existingshadow mask forming system, and a series of steps from a masking step toan etching process can be very efficiently continuously carried out. Thelaminated structure is washed with water, the resist film is removedwith an alkali solution, the laminated structure is washed again, andthen the laminated structure is dried.

Coloring Preventing Effect:

An etchant is sprayed on the entire surface of the laminated structure,and all the layers including the metal layer 21 are exposed to thecorrosive action of the etchant. After the openings 105 have beenformed, the adhesive layer 13 is exposed to the etchant and hence it ispossible that the adhesive layer 13 is colored with the etchant. If theadhesive layer 13 is colored, L*, a* and b* of color tone expressed bycolor system “L*, a*, b*, ΔE*” specified in Z 8729, JIS increase anddeteriorate the visibility of images.

The present invention can leave the antirust layer 25A on the side ofthe base 11 in the openings 105 as well as on the lines 107 to protectthe adhesive layer 13 by the antirust layer 25A form the corrosiveaction of the etchant. Consequently, the adhesive layer 13 is notcolored and hence the visibility of images is not deteriorated. Adhesionof the conductive structure 109 to the flattening layer 29 is notdecreased.

Peeling Preventing Effect:

It is possible that the adhesive layer 13 is caused to come off due tothe agency of the alkali solution when the alkali solution is used forremoving the resist film 109 a after etching. Since parts of theantirust layer 25 a remain in the openings 105 of the meshed pattern,the adhesive layer 13 is protected by the antirust layer 25A from theadverse effect of the alkaline resist removing solution.

Contamination Preventing Effect:

Usually, the adhesive layer 13 is contaminated with iron and sodiumcontained in the etchant. The antirust layer 25A protects the adhesivelayer 13 from contamination with the etchant. The surface of theelectromagnetic shielding sheet 1 with the adhesive layer 13 notcontaminated with iron and sodium is free from wetting that sometimesoccurs when the electromagnetic shielding sheet 1 is disposed in frontof a display in a hot, humid environment, and have an excellentappearance. Although the reason why the electromagnetic shielding sheet1 has such properties is not definitely known, it is inferred that theantirust layer 25A containing a metal oxide as a principal component hasa high surface tension and has high wettability. The formation of theantirust layer 25A also in the openings 105 a provides special functionsand effects.

Mesh structure:

The mesh structure 103 has the lines 107 defining the openings 105.There are not particular restrictions on the shape of the openings 105.The openings 105 may have a triangular shape, such as the shape of anequilateral triangle or an isosceles triangle, a quadrilateral shape,such as the shape of a square, a rectangle, a rhombus or a trapezoid, apolygonal shape, such as the shape of a pentagon, a hexagon or anoctagon, a circular shape or an elliptic shape. The openings 105 form amesh.

The width W of the straight parts of the lines 107 of the mesh structure103 is within C(1±30%), where C is a predetermined value, and the radiusof curvature of a side surface extending between the upper and the lowerside of a bank in a section of the lines 107 in a plane perpendicular tothe transparent sheet 11, i.e., the side surface surrounding theopenings 105, is in the range of 1.5 to 3.0 times the thickness of themetal layer in view of ratio of open area, mesh invisibility and imagevisibility. Preferably, the width W of the lines 107 of the meshstructure 103 is between 5 and 25 μm, and the pitches between the lines107 are between 150 to 500 μm. The width of a peripheral part of themesh structure 103 may correspond to between 1 to 50 meshes or lines 107in a peripheral part of a width between 0.15 to 15 mm may have a widthoutside the foregoing range of C(1±30%).

Generally, an electromagnetic shielding sheet for a large plasma displaypanel has thousands of intersecting straight lines. The lines 107 areformed such that the widths thereof are distributed within a desiredwidth range and the radius of the side surface of a bank extendingbetween the upper and the lower side of a section in a planeperpendicular to the transparent sheet 11 is controlled. Theelectromagnetic shielding sheet 1 meeting those conditions has anelectromagnetic shielding ability, a proper transparency, uniformlyarranged meshes, a few black and white spot defects and linear defects,a surface that does not glare or suppresses the reflection of externallight, and enables images to be seen in excellent visibility.

The range of distribution of widths of the lines 107 having, forexample, a nominal line width of 14 μm is between 9.8 to 18.2 μm. Whenthe widths of the lines 107 are within this range, the lines 107 do notform meshes in an irregular density, and do not form undesirable blackand/or white spot defects and linear defects. If the widths of the lines107 are distributed in an excessively wide width range, the meshes areformed in an irregular mesh density. Parts, in which the lines 107 havean excessively wide width, of the electromagnetic shielding sheet formundesirable black spot defects, and parts, in which the lines 107 havean excessively narrow width, of the electromagnetic shielding sheet formundesirable white spot defects. White and/or black spot defects make theviewer feel a very strong feeling of wrongness.

The laminated structure 103 of the electromagnetic shielding sheet 1 ofthe present invention is formed by a continuous photolithographicprocess, has the lines having widths within the predetermined widthrange. Therefore, meshes of the mesh structure 103 are not formed in anirregular mesh density, and the electromagnetic shielding sheet 1 has asatisfactory electromagnetic shielding ability and a propertransparency. The irregular mesh density, the black and/or white spotsand the linear defects are formed if a spray of the resist adheres toparts other than those to be coated with the resist. Such a troublerarely occurs in the continuous photolithographic process.

A peripheral part contiguous with the circumference of the meshstructure 103 may be excluded from those for which the width W of thelines 107 is controlled. That is, the grounding frame 101 formed of themetal layer 21 and surrounding the mesh structure 103 does not have anylines 107 and, in some cases, end parts of the lines 107 in theperipheral part are widened toward the grounding frame 101. The width ofthe peripheral part of the mesh structure 103 corresponds to between 1to 50 meshes or is between 0.15 to 15 mm, preferably, corresponds tobetween 1 to 25 meshes or is between 0.3 to 7.5 mm.

A suitable resist is selected and conditions of the etching process aredetermines so as to form the lines 107 such that the radius of curvatureof a side surface extending between the upper and the lower side of abank in a section of the lines 107 in a plane perpendicular to thetransparent sheet 11 is in the range of 1.5 to 3.0 times the thicknessof the metal layer and the width W of the lines 107 of the meshstructure 103 is within the range of C(1±30%), where C is apredetermined value. For example, it is desirable that a dry resist or aliquid resist is used, an etchant having a Baumé degree of 35° or aboveis used, a ferric chloride solution or a cupric chloride solution heatedat 35° C. or above is used as the etchant, the etchant is splayed at aspraying rate of 2000 ml/min or above, and a spray nozzle is oscillatedin a vertical or horizontal plane.

The radius of curvature and the line width of the lines 107 can beeasily controlled by forming the lines of the pattern in a width greaterthan the line width of the lines 107 to increase the amount of parts tobe etched and etching the laminated structure 109 at a low etch rate.

The radius of curvature of a side surface extending between the upperand the lower side of a bank is estimated from the lengths of sides ofan electron micrograph, taken at a 2000× magnification, of the line 107in a specimen obtained by slicing the electromagnetic shielding sheet ina plane perpendicular to the transparent base 11 with a microtome in aslice, and coating the slice with a platinum-palladium alloy bysputtering. The section of banks formed by etching does not necessarilyhave a truly circular shape. The line representing the side surface ofthe bank may be a line similar to the circumference of a substantiallycircular shape or an inclined side of a trapezoid.

In brief, it is desired that the radius of curvature of a line segmentextending between the respective right ends of the upper and the lowerside or a line segment extending between the respective left ends of theupper and the lower side is between 1.5 to 3.0 times the thickness ofthe metal layer. The radius of curvature does not necessarily need to befixed and may be varied, provided that the same is within the range of1.5 to 3.0 times the thickness of the metal layer.

Although the lines 107 shown in FIG. 1 are bias lines inclined to thelower side of the electromagnetic shielding sheet at 45°, the angle ofthe lines 107 to the lower side is not limited thereto and may beselectively determined taking into consideration the light emittingcharacteristic of the associated display and the arrangement of pixelsto prevent the formation of moiré.

Flattening:

the lines 107 of the mesh structure have a height corresponding to thethickness of the metal layer 21, and parts of the metal layer 21 areremoved to form the openings 105. The openings 105 are recessessurrounded by the lines 107. Thus, the conductive structure 109 has anirregular surface. When an adhesive (or a pressure-sensitive adhesive)is applied to the irregular surface of the conductive structure 109 bythe next process, the openings 105 are filled up with the adhesive. Ifthe conductive structure 109 is attached to the surface of a member,such as the screen of a display, immediately after the formation of themesh structure, the irregular surface having the exposed recessesobstruct work for applying the conductive structure 109 to the member,it is possible that bubbles are contained in the openings 105, theinterfaces between the bubbles and the adhesive scatter light toincrease haziness and whitening. Therefore, it is desirable to flattenthe surface of the conductive structure 109 by filling up the recesses.

The recesses are filled up with a transparent resin for flattening.Bubbles are contained in the transparent resin to decrease transparencyunless the recesses are filled up completely with the transparent resin.Therefore, a transparent resin diluted with a solvent and having a lowviscosity is applied to the surface of the conductive structure 109 in aresin film, and the resin film is dried to form the flattening layer 29,or the resin is applied to the surface of the conductive structure 109,deaerating the same to form the flattening layer 29.

The flattening layer 29 may be formed of any suitable resin, providedthat the resin has a high transparency, and sufficiently adhesive to themetal forming the mesh structure and to an adhesive to be used by thenext process. If projections or recesses are formed in the surface ofthe flattening layer 29 and the surface of the flattening layerundulates, the flattening layer 29 exercises an unsatisfactorybubble-eliminating effect when an adhesive is applied to the surface ofthe flattening layer 29 and the flattening layer 29 is attached to aholding member 32. If the surface of the flattening layer 29 is notsatisfactorily flat, moiré, interference fringes and/or Newton rings areformed when the electromagnetic shielding sheet is disposed in front ofa display. It is preferable to apply a thermosetting or UV-curable resindiluted by a solvent and having a low viscosity to the conductivestructure 109 so that the recesses forming the openings 105 are filledup completely and a resin layer is formed, to remove the solvent fromthe resin layer by drying, to attach a flat release sheet to the surfaceof the resin layer, to cure the resin layer by heating or irradiationwith UV radiation, and to remove the release sheet from the cured resinlayer. The flat surface of the release sheet is transferred to theflattening layer 29 to form a flat surface. The release sheet is, forexample, a biaxially oriented polyethylene terephthalate film coatedwith a releasing layer of a silicone resin.

The flattening layer 29 may be formed of any suitable resin, such as anatural resin, a synthetic resin, a thermosetting resin or anionizing-radiation-curable resin. In view of durability, applicabilityand flattening property, suitable materials for forming the flatteninglayer 29 are prepolymers or oligomers including urethane (meth)acrylateresins, polyester (meth)acrylate resins, and epoxy (meth)acrylateresins, monomers including trimethylolpropane (meth)acrylate resins,dipentaerythritol hexa(meth)acrylate resins, and UV-curable resinsprepared by mixing some of those prepolymers and the monomers.

Near-infrared-absorbing Agent:

Preferably, the resin forming the flattening layer 29 contains anear-infrared-absorbing agent capable of absorbing near-infraredradiation in a specific wave band. The flattening layer 29 containingthe near-infrared-absorbing agent absorbs near-infrared radiation in thespecific wave band to shield the near-infrared radiation radiated by thedisplay so that apparatuses controlled by near-infrared radiationemitted by remote controllers or the like may not malfunction due to thenear-infrared radiation. The specific wave band of the wavelengths ofnear-infrared radiation is between about 780 to about 1200 nm. It isparticularly desirable to absorb 80% or above of near-infrared radiationhaving wavelengths in a wave band of 800 to 1100 nm. Any suitablenear-infrared-absorbing agent may be used. A suitablenear-infrared-absorbing agent is, for example, a coloring matter havingpeak electromagnetic absorption wavelengths in the near-infrared waveband, a high light transmittance in the visible region and not having aspecific peak electromagnetic absorption wavelength in the visibleregion. Suitable near-infrared-absorbing agents are phthalocyaninecompounds, immonium compounds, di-immonium compounds and dithiol metalcomplex compounds. Although those near-infrared-absorbing agents may beindividually used, it is preferable to use a blend of some of thosenear-infrared-absorbing agents. For example, a blend of a di-immoniumcompound and a phthalocyanine compound is used. Usually, visible lightemitted by a PDP contains a large amount of orange light having aspectrum corresponding to the emission spectrum of neon atoms.Therefore, it is desirable that the flattening layer 29 contains a colortone correcting light-absorbing agent that absorbs some of visible lighthaving wavelengths in the range of about 570 to about 605 nm. Coloringmatters meeting such a requirement include cyanine compounds,phthalocyanine compounds, naphthalocyanine compounds, naphthoquinonecompounds, anthraquinone compounds and dithiol complexes. Either thenear-infrared-absorbing agent or the color tone correctinglight-absorbing agent, or both the near-infrared-absorbing agent and thecolor tone correcting light-absorbing agent are added to the materialforming the flattening layer 29 as the occasion demands.

Near-Infrared-Absorbing Layer:

The light-absorbing layers 31A and 31B capable of absorbingnear-infrared radiation are formed on the surfaces of the base 11 andthe flattening layer 29, respectively, or the light-absorbing layer 31Aand/or 31B is formed on the surface of the base 11 and/or the surface ofthe flattening layer 29. The light-absorbing layer 31A is formed on thesurface of the base 11, and the light-absorbing layer 31B is formed onthe surface of the flattening layer 29 as shown in FIG. 1. Thelight-absorbing layers 31A and 31B may be near-infrared-absorbing filmson the market, such as Film No. 2832 commercially available from Toyobo,bonded to the base 11 and the flattening layer 29 with an adhesive ormay be films of a binder containing the aforesaidnear-infrared-absorbing agent. Suitable binders include polyesterresins, polyurethane resins, acrylic resins and thermosetting orUV-curable resins utilizing the reaction of epoxy groups, acrylategroups, methacrylate groups or isocyanate groups.

Generally, the electromagnetic shielding sheet of the present inventionis laminated to the holding member 32 with an adhesive layer. Theholding member 32 is a transparent substrate (protective layer or areinforcing layer), a functional sheet with an antireflection layer, ahard coating layer, an antifouling layer and/or an antiglare layer orthe screen of a display. The holding member 32 may be on the side ofeither the base 11 or the conductive structure 109. Holding members 32may be on the side of both the base 11 and the conductive structure 109.In FIG. 7, the holding member 32 is bonded to the conductive structure109 with an adhesive layer 33. In forming the adhesive layer 33, anadhesive must be carefully spread over the surface of the conductivestructure 109 so that air filling the openings is completely replacedwith the adhesive and any bubbles B may not be locked in the adhesivefilling up the openings. Locking of bubbles B in the adhesive layer 33can be prevented by forming the flattening layer 29 on the conductivestructure 109 and coating the surface of the flattening layer 29 withthe adhesive.

Antireflection Layer:

An antireflection layer may be formed on a surface, on the viewing side,of the electromagnetic shielding sheet. The antireflection layerprevents reflecting visible light. There are various commerciallyavailable single-layer and multiple-layer antireflection films. Amultiple-layer antireflection film consists of alternatehigh-diffraction and low-diffraction layers. Suitable high-diffractionlayers are those of niobium oxide, titanium oxide, zirconium oxide andITO. Suitable low-diffraction layers are those of silicon oxide,magnesium fluoride and such. Some antireflection film has a layer havinga minutely roughened surface that reflects external light in a diffusedreflection mode.

Hard Coating Layer, Antifouling Layer, Antiglare Layer:

A hard Coating layer, an antifouling layer and an antiglare layer may beformed on the antireflection layer. The hard coating layer has ahardness not lower than a hardness H determined by a pencil hardnesstest method specified in K 5400, JIS. The hard coating layer is formedby heating or irradiating with ionizing radiation a film of apolyfunctional (meth)acrylate resin, such as a polyester (meth)acrylateresin, a urethane (meth)acrylate resin or an epoxy (meth)acrylate resin.The antifouling layer is a water-repellent, oil-repellent coating of asiloxane compound or a fluorinated alkylsilyl compound. The antiglarelayer has a minutely roughened surface capable of reflecting externallight in a diffused reflection mode.

Cutting:

A continuous base sheet on which electromagnetic shielding structuresare formed is unwound from a roll and the continuous base sheet is cutto provide individual electromagnetic shielding sheets 1. A front platefor a display is formed by attaching the electromagnetic shielding sheet1 to a holding member, i.e., a transparent substrate of glass or aresin. When necessary, an antireflection layer, a hard coating layer, anantifouling layer and/or an antiglare layer is laminated to theelectromagnetic shielding sheet 1. A rigid transparent substrate of athickness in the range of 1 to 10 mm is used for forming a front panelfor a large display. A resin film of a thickness in the range of 0.01 to0.5 mm is used as a transparent substrate for forming a front panel fora small display, such as a character indicator or the like. Thus, aproper transparent substrate is used selectively according to the sizeand use of the display. The electromagnetic shielding sheet 1 may bedirectly applied to the screen of a display.

Direct Application:

Direct application of the electromagnetic shielding sheet 1 to thescreen of a display will be described. The electromagnetic shieldingsheet 1 is attached to the screen of a display with the mesh metal layerfacing the viewing side, and at least a blackened layer is formed on themetal layer. When the electromagnetic shielding sheet 1 is thus attachedto the display, the grounding frame 101 is exposed and can be easilyconnected to a ground. The flattening layer 29 is not formed over thegrounding frame 101. The very thin antirust layer 25B and the very thinblackened layer 23B do not obstruct grounding the grounding frame 101.Since the grounding frame 101 is processed by the blackening process andfaces the viewing side, the front glass plate does not need any printed,black frame, which reduces processes and has an advantageous effect oncost reduction.

Examples will be described.

EXAMPLE 1

A 10 μm thick electrolytic Cu foil was used as a conductive structure109 including a metal layer 21. Blackened layers 23A and 23B of Co—Cualloy particles having a mean particle size of 0.3 μm, and chromatedlayers 25A and 25B were formed on the Cu foil. A 100 μm thicktransparent, biaxially oriented PET film A4300® (Toyobo) as a base waslaminated to the chromated surface of the Cu foil with a two-partpolyurethane adhesive. A structure formed by laminating the PET film andthe Cu foil was aged at 56° C. for four days. The two-part adhesiveincludes TAKERAKKU A-310® (polyol) (Takeda Yakuhin Kogyo) as an adhesiveresin, and Hardener A-10® (isocyanate) (Takeda Yakuhin Kogyo) as ahardener. The two-part adhesive was spread in a 7 μm thick film in a drystate. The chromating process used a 0.1% ALSURF 1000® (Nippon Paint)solution as a chromating solution. The structure was immersed in thechromating solution heated at 40° C. for 1 min, the chromated structurewas washed and the washed, chromated structure was dried at 80° C. for10 min.

The structure formed in a continuous laminated film was masked andetched by a photolithographic process. The photolithographic process wascarried out by a shadow mask manufacturing line for manufacturing shadowmasks for color TV sets. A photoresist film of casein was formed overthe entire surface of the conductive structure of the laminated film bya flow coating method. The laminated film was delivered to the nextstation. The laminated structure was exposed to light emitted by amercury lamp through a photomask having a pattern for forming 22 μm widelines defining square openings, arranged at pitches of 300 μm andinclined at 49°, and 5 mm wide grounding parts. The laminated structurewas processed at the following stations for developing, hardening andburning at 80° C.

Subsequently, parts of the Cu foil and those of the blackened layercorresponding to the openings were removed by an etching process using aferric chloride solution heated at 40° C. and having a Baumé degree of40° as an etchant by a spray etching method having a side etchingeffect. Thus, the openings were formed without etching the chromatedlayer on the side of the base. The laminated film was processed by thefollowing processes at the following stations for washing, resist filmremoval, rinsing and drying at 80° C. to complete electromagneticshielding sheets in Example 1.

EXAMPLE 2

Electromagnetic shielding sheets in Example 2 were the same as those inExample 1, except that the chromated layers of the electromagneticshielding sheets in Example 2 contained zinc oxide.

EXAMPLE 3

Electromagnetic shielding sheets in Example 3 were the same as those inExample 1, except that the electromagnetic shielding sheets in Example 3were provided with nickel oxide layers formed by plating instead of thechromated layers.

EXAMPLE 4

Electromagnetic shielding sheets in Example 4 were the same as those inExample 1, except that the electromagnetic shielding sheets in Example 4were provided with nickel oxide layers and zinc oxide layers formed byplating instead of the chromated layers.

EXAMPLE 5

Electromagnetic shielding sheets in Example 5 were the same as those inExample 1, except that the electromagnetic shielding sheets in Example 5were provided with nickel oxide layers, zinc oxide layers and copperoxide layers formed by plating instead of the chromated layers.

COMPARATIVE EXAMPLE 1

Electromagnetic shielding sheets in Comparative example 1 were the sameas those in Example 1, except that the electromagnetic shielding sheetsin Comparative example 1 were not provided with any layer correspondingto the chromated layer 25A on the side of the base 11 of theelectromagnetic shielding sheets in Example 1.

EXAMPLE 6

Electromagnetic shielding sheets in Example 6 were fabricated by thesteps of coating the surfaces of the mesh structures of theelectromagnetic shielding sheets in Example 1 with a film of aflattening composition, laminating a 50 μm thick SP-PET20-BU® (Tosero),i.e., a PET film having a surface having a release characteristic, tothe surface of the film of the flattening composition, exposing the thuscoated electromagnetic shielding sheets to radiation of an intensity of200 mj/cm² (in terms of 365 nm) emitted by a high-pressure mercury lamp,and removing the SP-PET20-BU. The electromagnetic shielding sheets inExample 6 had a flattening layer of the flattening composition fillingup the openings of the mesh structures.

The flattening composition was prepared by mixing 20 parts by mass ofN-vinyl-2-pyrrolidone, 25 parts by mass dicyclopentenyl acrylate, 52parts by mass oligoester acrylate (M-8060®, Toa Gosei), and 3 parts bymass 1-hydroxycyclohexyl phenylketone (IRUGACURE 184, ciba-Geigy).

EXAMPLE 7

Electromagnetic shielding sheets in Example 7 were the same as those inExample 6, except that a flattening composition used by Example 7contained 1 part by mass thiol-nickel complex in addition to thecomponents of the flattening composition used by Example 6.

EXAMPLE 8

Electromagnetic shielding sheets in Example 8 were the same as those inExample 6, except that NIR Film No. 2832® (Toyobo), i.e., anear-infrared absorbing film, was laminated to the flattening layer withan adhesive.

EXAMPLE 9

Electromagnetic shielding sheets in Example 9 were the same as those inExample 1, except that the electromagnetic shielding sheets in Example 9were not provided with any layer corresponding to the chromated layer ofCu—Co alloy particles, and were provided with a PET film laminatedthereto and a flattening layer similar to that of Example 6.

The electromagnetic shielding sheets in Examples 1 to 9 and ComparativeExample 1 were mounted on PDPs. The visibility of images displayed bythe PDP was evaluated through the visual observation of the displayedimages, and near-infrared absorbing abilities of the electromagneticshielding sheets were measured.

Images displayed by the PDPs provided with the electromagnetic shieldingsheets in Examples 1 to 8 did not glare, white and/or black spot defectsand linear defects were not found in the images, images did not haze(whitened), and the visibility of the images was satisfactory.Near-infrared transmittances in the wave band of 800 to 1100 nm measuredby a spectral transmittance recorder were less than 20%. When theelectromagnetic shielding sheet in Example 9 was attached to the PDPwith the base adhesively bonded to the surface of the PDP, aninsignificant amount of stray light rays was produced by reflectinglight emitted by the PDP, the surface of the PDP did not glare, thevisibility of images displayed by the PDP was satisfactory, work forconnecting the electrode was reduced and the glass substrate did notneed any printed black frame.

The adhesive layers of Examples 1 to 9 were analyzed by FluorescentX-ray Spectroscope RIX3000® (Rigaku) to measure Fe and Na. The adhesivelayers did not contain Fe and Na at all. Parts corresponding to theopenings were neither clouded nor colored. Any abnormalities did notoccur when the PDPs provided with the electromagnetic shielding sheetsin Examples 1 to 9 were operated continuously for ten hours.

Parts, corresponding to the openings, of the electromagnetic shieldingsheets in Comparative example 1 were clouded slightly, images displayedby the PDPs provided with the electromagnetic shielding sheets inComparative example 1 had low contrast, and the visibility of images wasunsatisfactory.

The electromagnetic shielding sheets of the present invention aredisposed in front of displays, such as CRTs and PDPs to shieldelectromagnetic radiation generated by the displays, the invisible linesof the mesh structure have both an electromagnetic shielding ability anda high transparency. The electromagnetic shielding sheets of the presentinvention can be used with either of its opposite surfaces facing theviewing side and enable satisfactory visual observation of displayedimages.

1. An electromagnetic shielding sheet comprising: a transparent base; atransparent antirust layer formed on one of the surfaces of the base;and a mesh metal layer formed on the antirust layer and having linesdefining openings; wherein the antirust layer extends over parts of thebase corresponding to both the lines and the openings, and the openingsin the mesh metal layer are filled up with a transparent resin such thatthe surface of the transparent resin is flush with the surface of themetal layer.
 2. The electromagnetic shielding sheet according to claim1, wherein the lines of the metal layer have a width in the range of 5to 25 μm and are arranged at pitches in the range of 150 to 500 μm. 3.The electromagnetic shielding sheet according to claim 1, wherein ablackened layer is formed on one of the surfaces of the metal layer. 4.The electromagnetic shielding sheet according to claim 1 furthercomprising an additional antirust layer formed on one surface of themetal layer opposite the other surface of the same facing the base. 5.The electromagnetic shielding sheet according to claim 4 furthercomprising a layer of a color tone correcting agent capable of absorbingvisible light having wavelengths in the range of 570 to 605 nm and/or alayer of a near-infrared-absorbing agent that absorbs near-infraredradiation having wavelengths in the range of 800 to 1100 nm formed onthe outer surface of either the base or the additional antirust layer.6. The electromagnetic shielding sheet according to claim 1, wherein thetransparent resin filling up the openings in the mesh metal layercontains a color tone correcting light-absorbing agent capable ofabsorbing visible light having wavelengths in the range of 570 to 605 nmand/or a near-infrared-absorbing agent capable of absorbing infraredradiation having wavelengths in the range of 800 to 1100 nm.